Electric lamp, and light projector provided with an electric lamp

ABSTRACT

An electric lamp ( 1 ) comprising an elliptical reflector body ( 3 ) with a light emission window ( 5 ) and with a light-transmitting cover ( 11 ) positioned in the light emission window. A light chamber ( 7 ) is defined by the reflector body, in which chamber a light source ( 13 ) is positioned in a first focus (F 1 ) of the reflector body. A second focus (F 2 ) of the reflector body is located outside the light chamber and at an end ( 19 ) of an optical waveguide ( 17 ). The cover is provided with IR-reflecting means ( 15 ) and is parabolically or elliptically shaped, the cover having a focus (Flid) which is located on the light source.

The invention relates to an electric lamp comprising:

-   -   an elliptical reflector body comprising a light emission window        and surrounding a light chamber, and having a first focus in the        light chamber and a second focus outside the light chamber,    -   a reflector coating provided on the reflector body, which        coating reflects visible light;    -   a light-transmitting cover connected to the reflector body at        the area of the light emission window;    -   a light source arranged in the light chamber in the location of        the first focus.

The invention also relates to a light projector.

Such an electric lamp is known from U.S. Pat. No. 4,041,344. The knownlamp is suitable for coupling light, originating from the light sourceand reflected in a desired direction by the reflector coating, into anend of an optical waveguide, such as an optical fiber, which ismanufactured, for example, from synthetic resin. The end of the fiber isfor this purpose located in the second focus of the ellipticalreflector. It is achieved thereby that radiation originating from acomparatively large light source can be coupled into the opticalwaveguide and can thus be concentrated into a comparatively narrow lightbeam of comparatively high intensity. It is a disadvantage of the knownelectric lamp that this method of coupling gives the optical waveguide ahigh degree of heating at its end because of the high intensityobtained, which thus leads to a comparatively high risk of deformationand/or loss of its comparatively favorable coupling and wave-guidingproperties.

The invention has for its object to counteract the above disadvantage.For this purpose, the electric lamp of the kind described in the openingparagraph is characterized in that the light-transmitting cover isprovided with means for blocking infrared (IR) radiation. Heating-up ofthe optical waveguide is caused in particular by infrared radiationwhich is generated in addition to visible light by the light sourceduring operation of the light source. The means for excluding IRradiation counteract that this IR radiation is coupled into the opticalwaveguide. It is achieved thereby that the optical waveguide is heatedto a substantially lesser degree. The means for excluding IR radiationmay be, for example, a glass which absorbs IR radiation and from whichthe cover is manufactured. Alternatively, the means for excluding IRradiation may comprise an infrared-reflecting coating, for example adichroic coating. The coating may be an interference coating which ismirroring and which is built up from alternating layers of comparativelyhigh and comparatively low refractive index, for example titaniumdioxide and silicon dioxide, respectively. It can be achieved in asimple manner thereby that the IR radiation is displaced towards adesired location by reflection, for example towards the light source. Toachieve this, the cover of a favorable embodiment of the electric lampis elliptically or parabolically curved. Preferably, the ellipticallycurved cover has two focuses in the electric lamp, each being located onthe light source. Not only does this counteract the undesirable heatingof the optical waveguide, it also achieves that the reflected IRradiation is usefully employed for heating the light source. Acomparatively efficient operation of the light source is thus achieved.A similar argument holds for a parabolically curved cover, of which afocus is located on the light source.

In an alternative embodiment, the cover is not only infrared-excluding,but in addition red or amber in color. Such a colored cover makes itpossible to use the electric lamp in vehicles, for example automobiles,for example as a brake light and/or indicator light. The red or ambercolor of the cover may be achieved by means of a red or amber coating,but it is alternatively possible for the cover to be manufactured from ared or amber material.

In a favorable embodiment, the reflector coating transmits infraredradiation. Such a property of the reflector coating can be realized in acomparatively simple manner, for example by the use of a dichroiccoating as the reflector coating, and has the advantage that the heat ofthe light source is guided away from the optical waveguide. Thereflector coating may be provided either on an inner surface or on anouter surface of the reflector body.

The light source may be a filament, while the light chamber is gastightand filled with an inert gas, which gas may or may not comprise ahalogen. A filament used in this manner has the advantage that lightoriginating from the light source is free from disturbances in theoptical path of the light such as may occur when a filament is used in aseparate bulb.

Alternatively, the light source may comprise a separate discharge bulbin which a pair of electrodes is positioned one opposite the other, thusdefining a discharge path. The discharge path in that case is located inthe first focus of the reflector in the light chamber. It isalternatively possible for the light source to comprise a separate,gastight bulb with a filament therein, which filament is located in thefirst focus of the reflector body in the light chamber. A separate bulbhas the advantage that, in the case of failure of the light source, itsuffices to replace the bulb and the light source in a comparativelysimple manner so as to make the electric lamp operational again.

An embodiment of the electric lamp according to the invention will beexplained in more detail with reference to the diagrammatic drawing inwhich:

FIG. 1 is a cross-sectional view of a first embodiment of an electriclamp according to the invention, and

FIG. 2 is a cross-sectional view of a second embodiment of an electriclamp according to the invention.

FIG. 1 is a cross-sectional view of an electric lamp (1) comprising anelliptical reflector body (3) with a light emission window (5) andsurrounding a light chamber (7). An ellipse (23) is shown with a dottedline, and it is indicated that the reflector body coincides with part ofthis ellipse. The reflector body has a first focus (F1) in the lightchamber and a second focus (F2) outside the light chamber. A reflectorcoating (9) which reflects visible light is provided on an outer side ofthe reflector body. A light-transmitting cover (11) is connected to thereflector body at the area of the light emission window, closing off thelight chamber in a gastight manner. A light source (13), a filament inthe Figure, is arranged in the light chamber in the location of thefirst focus. The light-transmitting cover is provided with means (15)for excluding infrared radiation, a dichroic coating in the Figure builtup from alternating layers of titanium dioxide and silicon dioxide. FIG.1 also shows an optical waveguide (17) which is positioned with one end(19) in the second focus (F2) of the reflector body. The cover has anelliptically curved shape with two focuses Flid which are located on thefilament. Infrared radiation incident on the cover is accordinglyreflected by the cover onto the filament.

FIG. 2 is a cross-sectional view of a second embodiment of an electriclamp (1) according to the invention. The light source (13) in the Figureis a gas discharge lamp, i.e. a pair of electrodes surrounded by a bulb(19) and positioned such that the first focus (F1) of the reflector body(3) lies between the electrodes forming the electrode pair. Tocounteract light losses, the bulb is partly provided with alight-reflecting coating (21). A light-transmitting cover (11) isconnected to the reflector body at the area of the light emission window(5) and is manufactured from an amber-colored glass and is provided withmeans for excluding infrared radiation. The reflector body is providedwith a reflector coating (9) on an inner surface, which coating reflectsvisible light and transmits infrared radiation.

1. An electric lamp (1) comprising: an elliptical reflector body (3)comprising a light emission window (5) and surrounding a light chamber(7), and having a first focus (F1) in the light chamber and a secondfocus (F2) outside the light chamber, a reflector coating (9) providedon the reflector body, which coating reflects visible light; alight-transmitting cover (11) connected to the reflector body at thearea of the light emission window; a light source (13) arranged in thelight chamber in the location of the first focus, characterized in thatthe light-transmitting cover is provided with means (15) for blockinginfrared (IR) radiation.
 2. An electric lamp as claimed in claim 1,characterized in that the means for excluding infrared radiationcomprise an infrared-reflecting coating.
 3. An electric lamp as claimedin claim 1, characterized in that the cover is red or amber in color. 4.An electric lamp as claimed in claim 2, characterized in that thereflector coating transmits infrared radiation.
 5. An electric lamp asclaimed in claim 1, characterized in that the cover is an ellipticallyor parabolically curved cover.
 6. An electric lamp as claimed in claim5, characterized in that the cover is elliptically curved and has twofocuses (F_(lid)), each focus being located on the light source.
 7. Anelectric lamp as claimed in claim 5, characterized in that the cover isparabolically curved and has a focus (F_(lid)) which is located on thelight source.
 8. A light projector comprising an electric lamp (1) asclaimed in claim 1, and an optical fiber (17) whose end (19) is locatedin the second focus (F2) of the elliptical reflector (3).